This is what I was able to find:
"In February of 1942, the Coast Guard adopted the Navy's ship classification system whereby a vessel was designated with a two-letter abbreviation (based on the type of ship) and its hull number. Thus, the large, sea-going cruising cutters of the first class became gunboats, or "PG." To differentiate them from their Navy counterparts, all Coast Guard cutters were given the prefix "W" at that same time. (The W was an unused letter on the Navy's designation alphabet and was arbitrarily assigned to designate a "Coast Guard cutter"--it does not stand for any particular word.) The Coast Guard also began assigning an exclusive hull number to each cutter."
SN Levesque, Michelle
STA Southwest Harbor, ME
Future BM